In clinical diagnosis, which employs a biological sample such as whole blood, serum, plasma, or urine, the measurement of a component to be measured in the biological sample is practiced. The component to be measured in the biological sample is measured by, for example, an enzymatic method or immunoassay using antigens and antibodies. The enzymatic assay of the component to be measured in the biological sample often involves converting the component to be measured into hydrogen peroxide by the action of oxidase, then reacting the formed hydrogen peroxide, in the presence of a peroxidase, with an oxidative-coloring chromogen, and measuring the absorbance of the resulting dye.
This measurement of the component to be measured in the biological sample based on the hydrogen peroxide quantification system is frequently used in continuous multi-sample measurement using an automatic analyzer, because of its mild reaction conditions, convenient operation, etc. This method, however, is susceptible to bilirubin, hemoglobin, or the like, present in the biological sample to disadvantageously receive a so-called negative influence, giving a measurement value lower than a theoretical value. To solve this problem, methods have previously been reported, such as a method using an iron-cyano compound (e.g., non-patent document 1).
Meanwhile, a surfactant is often used in the measurement of the component to be measured in the biological sample based on the hydrogen peroxide quantification system. The surfactant is used for a control of an enzyme specificity based on an interaction with a substrate of the enzyme, a control of an enzyme reactivity based on an interaction with the enzyme, the pretreatment of the sample, etc. Above all, polyoxyalkylene surfactants such as a polyoxyethylene surfactant or a polyoxypropylene surfactant is frequently used because of diversity of their types and availability.
Polyoxyalkylene surfactants, however, tend to form peroxides due to their structure (e.g., patent document 1). The peroxides formed have a disadvantageous positive influence on the hydrogen peroxide quantification system, thus giving a measurement value higher than a theoretical value. In particular, in cases where the conditions of storing a reagent or a kit for measuring biological samples are insufficient, peroxides are often formed in the reagent or kit, thereby causing deterioration in their performance.
In many cases, diagnosis kits comprise additives such as a salt, a buffer, an enzyme, and an antiseptic. Such kits may contain peroxides which are formed therein or come to be mixed from outside during the course of their production. In addition, peroxides may be formed by oxidation in such kits in the course of their prolonged storage. These peroxides may have a positive influence upon measurement using the kits. In addition, biological samples, such as whole blood, serum, plasma, or urine, may contain peroxides formed due to in vivo oxidative stress, enzyme reactions, administration of drugs, or the like. The peroxides so formed may have a positive influence upon measurement.
Pyruvic acid, one of α-keto acids, is formed as an intermediate product in the in vivo glycolytic system. The pyruvic acid is known to have relatively strong antioxidative activity (e.g., patent document 2). Also, its effect of neutralizing oxygen radicals in cells has been reported (e.g., patent document 3).
There is a demand for a measuring method whereby the influence of a peroxide is suppressed in the measurement of the component to be measured in the biological sample based on the hydrogen peroxide quantification system.